This invention relates to highly thixotropic ball-point inks having very low viscosities under writing conditions. These inks are particularly useful for computer plotter pens, which must travel at high speeds and change direction frequently and quickly.
Ball-point pens containing low viscosity inks have been commercially available since 1948. Because they write easily with little pressure and produce intense, opaque lines, they have attained commercial acceptance. Manufacturing such pens to uniform quality standards is difficult, however, for these reasons: (1) because their ink reservoirs are open to the atmosphere, their inks tend to evaporate, reducing shelf life; (2) because capillary action feeds ink to the ball of such pens, any break in the capillary ink channels from the reservoir to the ball of such pens causes them to stop writing; (3) sometimes, inks flow too rapidly from their reservoirs causing excessive ink to accumulate on the point of the pens; and (4) the absorbent felt-type ink reservoirs in these pens have small capacities.
Our new pressurized ball-point roller pens with their new inks overcome these problems. Because our ink cartridges are sealed, the inks cannot evaporate or dry out. Because our ink cartridges are pressurized, the inks feed dependably without requiring capillary action. Because our inks are gels while at rest, and because our inks are highly adhesive and viscoelastic, our inks do not ooze, and excessive ink seldom accumulates around the ball tip. Because our ink reservoirs are sealed and pressurized, they can hold a large quantity of usable ink.